1. Field of the Invention
This invention relates to electrochemical cells, and particularly to electrochemical cells that employ separate charging and discharging electrodes.
2. Description of the Prior Art
Electrochemical power sources are devices through which electric energy can be produced by means of electrochemical reactions. These devices include metal air electrochemical cells such as zinc air and aluminum air batteries. Certain metal air electrochemical cells employ an anode comprised of metal particles that are fed into the cell and consumed during discharge. Metal air cells include an anode, an air cathode, and an electrolyte. The anode is generally formed of metal particles immersed in electrolyte. The cathode generally comprises a semipermeable membrane and a catalyzed layer for reducing the oxidant, generally oxygen. The electrolyte is an ionic conductive but not electrically conductive material.
Metal air electrochemical cells have numerous advantages over traditional hydrogen-based fuel cells. In particular, the supply of energy provided from metal air electrochemical cells is virtually inexhaustible because the fuel, such as zinc, is plentiful and can exist either as the metal or its oxide. Further, solar, hydroelectric, or other forms of energy can be used to convert the metal from its oxide product back to the metallic fuel form. Unlike conventional hydrogen-oxygen fuel cells that require refilling, the fuel of metal air electrochemical cells is recoverable by electrically recharging. The fuel of the metal air electrochemical cells may be solid state, therefore, it is safe and easy to handle and store. In contrast to hydrogen-oxygen cells, which use methane, natural gas, or liquefied natural gas to provide as source of hydrogen, and emit polluting gases, the metal air electrochemical cells results in zero emission. The metal air cells operate at ambient temperature, whereas hydrogen-oxygen fuel cells typically operate at temperatures in the range of 80xc2x0 C. to 1000xc2x0 C. Metal air electrochemical cells are capable of delivering higher output voltages (1-3 Volts) than conventional fuel cells ( less than 0.8V).
One of the principle obstacles of metal air electrochemical cells is related to charging the cell, i.e., transformation of electrical energy to chemical energy, particularly after discharge, i.e., transformation of chemical energy to electrical energy. Ideally, charging and recharging should proceed nearly reversibly, be energy efficient, and result in minimum physical changes to the cell that may limit the operable life of the cell.
Therefore, it would be desirable to provide a rechargeable electrochemical cell and a recharging system that is efficient and minimizes cell component degradation.
The above-discussed and other problems and deficiencies of the prior art are overcome or alleviated by the several methods and apparatus of the present invention, wherein a rechargeable electrochemical cell system is provided. The system includes a plurality of cells, wherein each cell is comprised of a first electrode, a second electrode, and a third electrode electrically isolated from the second electrode. The cell system may be discharged upon application of a load across a discharge circuit, comprised of the first electrodes and the second electrodes. The cell may be recharged upon application of a voltage across a recharging circuit, comprised of at least one of the first electrodes and at least one of the third electrodes.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.